This invention relates to an ophthalmic gel. Various optically active medicaments have been topically applied to the eye for some considerable time. It is of course desirable to topically apply ophthalmic drugs to the eye, as opposed to other means of administration, since the drug will have less systemic side effects if applied directly to the eye. Also, the drug may well have increased activity if it can be applied at the site of use, rather than depending upon delivery in vivo such as by route of oral or injection administration. There are however problems attendant with the route of topical administration. One of those problems is the effectiveness of the ophthalmic drug permeating the cornea. Another of those problems is the ability of the drug to be maintined within the eye. There is the natural tendency of the tears to wash the drug out of the eye. This problem is magnified by movement of the eye itself and the surrounding muscle tissue of the eye socket. These movements tend to further enhance washing out of the ophthalmic drug.
Yet another problem attendant with ophthalmic delivery by topical administration is that if the drug in dosage form is thin and watery, it will often run out of the conjunctival sac of the eye before any effective delivery occurs. An even further problem can be confronted if one attempts to thicken the delivery carrier by conventional thixotropic agents, since many of those will cause eye irritation.
There is therefore a real and continuing need to develop ophthalmic gels which are comfortable in the conjunctival sac of the eye, which will not run out, and which will provide controlled drug release to the eye. The term "controlled drug release" means that the release level into the eye will be maintained at a relatively constant level over a sufficient period of time for effective administration to occur. It often happens that there is an initial burst release, or exaggerated dosage into the eye followed by a rapid drop off. This is undesirable for several reasons. First, the initial burst release has the propensity for increased side effects, since the dose is grossly exaggerated for a fleeting period of time. Secondly, a burst release is usually followed by a very low level release. This oftentimes will not provide the desired therapeutic effect. On the other hand, controlled sustained release, at a relatively constant dosage level, is desirable.
Accordingly, there is a real and continuing need for improved ophthalmic gels which provide for good ocular retention, while avoiding burst release of medicament, and yet providing controlled release of the medicament in order to provide increased delivery efficiency, and maximum therapeutic effect. One approach to this system is described in my previous U.S. Pat. No. 4,271,143, issued June 2, 1981, which relates to a carbopol gel for ophthalmic drug delivery. However, while that system is satisfactory for its preferred drug pilocarpine, the system is not satisfactory for other drugs. It does provide for sustained release over a prolonged period of time, but it also provides an initial burst release which is undesirable, particularly when used with other drug systems such as phenylephrine. The ophthalmic gel of the present invention does not provide for initial burst release and yet provides the advantages of controlled prolonged release.
The primary objective of the present invention is to provide an ophthalmic gel which provides good ocular retention while avoiding burst release and which at the same time provides controlled release of the medicament.
A further objective of the present invention is to provide an ophthalmic gel carrier which provides good ocular retention while avoiding burst release, and which provides controlled release of medicament, with the gel containing in combination sodium carboxymethyl-cellulose and colloidal magnesium silicate.
An even further objective of the present invention is to provide an ophthalmic gel for topical application which is especially adapted for use with a variety of medicaments, but most specifically adapted for use with the preferred medicament, phenylephrine.
A further objective of the present invention is to provide a stable ophthalmic gel which provides comfort to the patient when placed in the conjunctival sac of the eye.
An even further objective of the present invention is to provide an ophthalmic gel and method for using the same, which will avoid initial burst dosages of ophthalmic drug and thus decrease the risk of undesired patient side effects caused by initial burst release of drug.
The method and manner of accomplishing each of the above objectives, as well as perhaps others, will become apparent from the detailed description of the invention, which will follow hereinafter.